FIG. 7 shows a typical system of a welding robot using an articulated robot as an industrial robot. With reference to FIG. 7, a wrist portion 12 is formed at an end of a manipulator 11 configured by a plurality of arms. A welding torch 13, which is an end effecter, is attached to the distal end of the wrist portion 12. A welding wire is wound around a wire reel 14. The welding wire is passed through a conduit pipe 15 and supplied to the welding torch 13 by a wire feeder 16, which is attached to the manipulator 11. The conduit pipe 15 guides the welding wire from the wire reel 14 to the wire feeder 16. A single wire power cable 26, which is a torch cable, guides the welding wire from the wire feeder 16 to the welding torch 13.
The welding torch 13 receives power from a welding power source 17 through the single wire power cable 26 and shield gas from a gas cylinder 18. A teach pendant 19 inputs a command signal to a robot controller 10. The robot controller 10 inputs a signal to the manipulator 11. This rotates first to sixth axes of the manipulator 11, thus regulating the position of the distal end of the welding torch 13.
FIG. 8 shows the structure of a typical conventional welding torch 13. As illustrated in FIG. 8, a tip body 21 is attached to a torch body 20 of a welding torch 13. A power supply tip 22 is attached to a distal end 21a of the tip body 21. An insertion hole, through which a wire W is passed, is formed in a central portion of the power supply tip 22. The power supply tip 22 and the wire W contact each other to feed power to the wire W. A nozzle 23 is arranged around the power supply tip 22 and an orifice 24. The orifice 24 is arranged in such a manner as to substantially cover the circumferential surface of a distal portion of the tip body 21.
After having been supplied from the gas cylinder 18, the shield gas is ejected through the hole of the orifice 24. This shields an arc, a welding pool, and the vicinities of the arc and the welding pool from the nitrogen and the oxygen contained in the atmospheric air. An insulation bush 25 is attached to the outer circumferential surface of a central portion of the tip body 21.
However, in the welding torch configured as described above, spatter generated through arc welding adheres to the power supply tip, thus destabilizing the arc. Patent Document 1 proposes an apparatus that covers the circumference of a power supply tip by means of a tip cover to prevent spatter caused by arc welding from adhering to the power supply tip. Patent Document 2 proposes an apparatus having a cover with a wire insertion hole that is screwed to the distal end of a power supply tip of a welding torch.
In the welding torch 13, the power supply tip and the wire slide relatively on each other, and wear caused by such sliding cannot be avoided. This necessitates replacement of the power supply tip. However, in the apparatuses disclosed in Patent Documents 1 and 2, the power supply tip is screwed to and joined with the tip body and the tip cover is connected to the power supply tip through screwing or swaging. Accordingly, to replace the power supply tip, it is necessary to remove the power supply tip from the tip body and then the tip cover from the power supply tip. As a result, the welding torch having the tip cover covering the power supply tip has a disadvantage that the replacement of the power supply tip is complicated and cannot be accomplished easily.    Patent Document 1: Japanese Laid-Open Patent Publication No. 10-193124    Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-112261